This proposal describes a program to develop a small, portable, low-power electrochemical monitor to detect dissolved arsenic in drinking water. A non-toxic, renewable, microfabricated sensor chip integrated into a compact rnicrofluidic flow system is proposed and will be designed to detect both arsenate and arsenite in water based on a sensitive voltammetric method. This method will allow analysis of arsenic without significant dilution or reduction in the sensitivity of the detected analyte. The flow-cell sensor will use non-mercury microelectrodes which will enhance the sensitivity and limit of detection compared to conventional sized electrodes of millimeter dimensions. The device will also use a simple pump and valve system for both electrolyte and analyte introduction into the sensor and simple, proven electrochemical instrumentation for arsenic detection. Electrochemical detection of arsenic in aqueous samples is cost-effective and will find use for in situ monitoring of drinking water and surface waters. Our proposed monitor will eliminate the need to collect samples in the field for subsequent analysis and will be more sensitive than currently available colorimetric field kits.